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MONDAY, November 4, 2013 — The HPV vaccination is given in three shots, administered over a course of several months, but a new study suggests that just one dose might be sufficient to produce the immune system response that staves off human papillomavirus, which can cause cervical cancer. If the one-dose strategy stands up in subsequent clinical studies, it could mean that many more people could be vaccinated against HPV.

Researchers from the National Cancer Institute (NCI) in Bethesda, Maryland, have been studying a population of women in Costa Rica who had been given the vaccination, they reported in Cancer Prevention Research. Nearly 20 percent of the women missed subsequent doses after getting the first one, which prompted the researchers to investigate how the women's immune systems had reacted.

The HPV vaccine is made from one HPV gene, which programs the shape the virus will take. When the vaccine is administered, it acts like a disabled version of the virus, causing the body to produce an antibody response specific to HPV. The researchers found that even the women who had only received one dose of the vaccine still exhibited stable and strong HPV antibody levels.

“The results were definitely intriguing to us,” said study author Mahboobeh Safaeian, PhD, an investigator in the Division of Cancer Epidemiology and Genetics at the NCI. She thought that the HPV vaccine had been introduced in a three-part dosage form because previous vaccines of a similar nature had required multiple doses, but her results indicate it may be unnecessary. Current recommendations for HPV vaccine administration state that the second dose should be given two months after the first, and the third dose be given four months following the second.

“The minimum levels that are required for protection are not known yet,” Dr. Safaeian said. “The vaccine is highly efficacious, and induces a very strong immune response." Scientists need to do more research to determine what the lowest level that will still produce a robust response might be.

A study published in JAMA earlier this year suggested that two doses may be sufficient, said Mark Einstein, MD, gynecologic oncologist, Montefiore Medical Center and assistant professor of obstetrics, gynecology, and women’s health at Albert Einstein College of Medicine.

Safeaian noted that the women in her study received Cervarix, while the main vaccine used in the United States is Gardasil. But she thinks the results will apply to all HPV vaccines.

The NCI researchers focused on the developing world, since 85 percent of cervical cancer occurs there, she said. The possibility of giving only one dose be particularly meaningful in the developing world, since many countries rely on outside aid to bring in the vaccine, and only having to deliver only a single dose would be more efficient and cost effective.

The results have the largest implications for the developing world, Einstein agreed.

The results were surprising, and have implications for the science around vaccines, as well as specific implications for HPV vaccination, said Paula J Adams Hillard, MD, professor of obstetrics and gynecology at Stanford University and director of gynecology at the Lucile Packard Children’s Hospital at Stanford.

Currently, the CDC recommends that all boys and girls be vaccinated for HPV when they’re 11 or 12. The reasons parents often give for not getting their kids vaccinated are often complicated by the sexual implications of the vaccination (HPV is a sexually transmitted disease). For exmaple, some parents question how long the vaccination's effect will last and say they’re choosing to wait so their child will require fewer boosters.

In reality, the body responds better to the vaccine and produces a higher immune response when an individual is younger, Dr. Adams Hillard said. She added that she thinks the NCI study’s results may help resolve parents’ concern that getting the shot earlier will mean more follow-ups.

“This is an anti-cancer vaccine, and there’s not a lot that we can do to lower the risk of cancer,” said Adams Hillard. “This is it for HPV.”

Researchers still must rigorously test the theory that one dose is sufficient, and ultimately any changes to current recommendations would need to be reviewed by the CDC. The study authors are planning more research on the specific population in Costa Rica, to continue to test whether a single dose is effective.

While the results are promising, said Adams Hillard, it’s important to “stick with the current guidelines, and those guidelines say complete all three." This applies even if a person has lapsed in completing the dosing schedule. “Even if it’s been a while, go back and get the next in the series,” she said.

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